Squashed 'external/mio/' content from commit 8b6b7d8

git-subtree-dir: external/mio
git-subtree-split: 8b6b7d878c89e81614d05edca7936de41ccdd2da

include/mio/page.hpp

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+/* Copyright 2017 https://github.com/mandreyel
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this
+ * software and associated documentation files (the "Software"), to deal in the Software
+ * without restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to the following
+ * conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies
+ * or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+ * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+ * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
+ * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
+ * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef MIO_PAGE_HEADER
+#define MIO_PAGE_HEADER
+
+#ifdef _WIN32
+# include <windows.h>
+#else
+# include <unistd.h>
+#endif
+
+namespace mio {
+
+/**
+ * This is used by `basic_mmap` to determine whether to create a read-only or
+ * a read-write memory mapping.
+ */
+enum class access_mode
+{
+    read,
+    write
+};
+
+/**
+ * Determines the operating system's page allocation granularity.
+ *
+ * On the first call to this function, it invokes the operating system specific syscall
+ * to determine the page size, caches the value, and returns it. Any subsequent call to
+ * this function serves the cached value, so no further syscalls are made.
+ */
+inline size_t page_size()
+{
+    static const size_t page_size = []
+    {
+#ifdef _WIN32
+        SYSTEM_INFO SystemInfo;
+        GetSystemInfo(&SystemInfo);
+        return SystemInfo.dwAllocationGranularity;
+#else
+        return sysconf(_SC_PAGE_SIZE);
+#endif
+    }();
+    return page_size;
+}
+
+/**
+ * Alligns `offset` to the operating's system page size such that it subtracts the
+ * difference until the nearest page boundary before `offset`, or does nothing if
+ * `offset` is already page aligned.
+ */
+inline size_t make_offset_page_aligned(size_t offset) noexcept
+{
+    const size_t page_size_ = page_size();
+    // Use integer division to round down to the nearest page alignment.
+    return offset / page_size_ * page_size_;
+}
+
+} // namespace mio
+
+#endif // MIO_PAGE_HEADER